The disclosure of Japanese Patent Application No. 2001-133355 filed on Apr. 27, 2001 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to an apparatus and a method for controlling the amount of fuel injected into an internal combustion engine and, more particularly, to an apparatus and a method for controlling the amount of fuel injected into an internal combustion engine at the time of startup of the engine.
2. Description of the Related Art
When an internal combustion engine is started, that is, cranked, the amount of air taken into the engine is small and the intake pipe pressure is unstable, so that the amount of intake air cannot be accurately measured or estimated. Therefore, at the time of startup of the engine, a basic amount of fuel injected into engine is computed based on the temperature of cooling water of the engine, regardless of the amount of intake air. The basic amount of fuel injected at the time of startup of the engine is increased if the engine temperature is low, because lower engine temperature makes less likely the vaporization of fuel attached to a wall surface of the intake pipe. The basic amount of fuel injection is then corrected based on the engine rotation speed, the battery voltage, the ambient pressure, etc., so as to determine a final amount of startup fuel injection.
For example, Japanese Patent Application Laid-Open No. 9-53490 discloses a control apparatus that avoids an event that if the cranking rotation speed of an internal combustion engine becomes high at the time of very low engine temperature, the fuel vaporization rate increases and the air-fuel ratio in the intake pipe becomes an over-rich ratio so that the startup characteristic of an internal combustion engine deteriorates, by shifting a curve that determines a correction factor for correcting the startup-time basic fuel injection amount based on the engine rotation speed toward a lower engine rotation speed side at the time of very low engine temperature and therefore starting the correction of engine rotation speed at a lower rotation speed at the time of very low engine temperature than at the time of normal engine temperature.
As described above, the amount of fuel injected at the time of startup of the internal combustion engine is computed based on environmental conditions (atmospheric pressure and the like) and the states of the engine (cooling water temperature, rotation speed, battery voltage, etc.) at the time of startup. Thus, the startup-time fuel injection amount is basically a fixed amount of fuel injection that is independent of the amount of intake air. The amount of intake air at the time of startup of the internal combustion engine is determined by correcting an engine cooling water temperature-based startup-time basic amount of air through the use of a learned value of required amount of air (during idling) acquired by learning an amount of air needed to maintain a predetermined value of rotation speed of the engine during an idling operation subsequent to a warm-up of the engine.
The friction of the engine and the drive system of a vehicle gradually decreases from the levels of a new vehicle state. Therefore, the amount of air needed to maintain a certain idling rotation speed after a warm-up of the engine tends to gradually decrease from the new vehicle-state level. The amount of air needed during such a hot idling operation changes depending on the status of deposit on the throttle valve and the idling rotation speed control valve.
Since the startup-time amount of air is corrected based on the idling-time required amount of air as mentioned above, the startup-time amount of air changes in accordance with the idling-time required amount of air. Therefore, if a startup-time fuel injection amount is computed based on environmental conditions and states of the engine excluding the amount of intake air, the air-fuel ratio at the time of startup of the engine changes as the startup-time amount of air changes with changes in the idling-time required amount of air. Hence, the startability of the engine at the time of starting up the engine cannot be made stable. Furthermore, in view of reduction of HCs discharged from an engine at the time of a cold startup, stabilization of the air-fuel ratio at the time of startup of the engine has become an important issue.
Accordingly, it is an object of the invention to provide a startup-time fuel injection amount control apparatus for an internal combustion engine which is capable of correcting a startup-time fuel injection amount in accordance with changes in the amount of intake air at the time of startup of the engine.
In order to achieve the aforementioned object, a control apparatus for controlling an amount of fuel injected into an internal combustion engine in accordance with an aspect of the invention and a control method thereof determine a required amount of air introduced into the internal combustion engine which is needed to maintain a predetermined value of rotation speed of the internal combustion engine during an idling operation after a warm-up of the internal combustion engine, and control the amount of air introduced into the internal combustion engine at a startup time of the internal combustion engine in accordance with the required amount of air, and control the amount of fuel injected into the internal combustion engine at the startup time of the internal combustion engine based on at least the required amount of air.
In general, if the amount of air needed to maintain a constant idling rotation speed of an internal combustion engine changes, the amount of air introduced into the internal combustion engine at the time of a startup of the engine also changes. According to the above-described control apparatus of the invention, the startup-time fuel injection amount is corrected in accordance with changes in the required amount of air during an idling operation of the engine, so that the startup characteristic of the internal combustion engine can be improved.
In the above-described apparatus of the invention, the amount of fuel injected into the internal combustion engine may be computed based on a startup-time internal combustion engine state that is other than the amount of air introduced into the internal combustion engine, and the computed amount of fuel injected may be corrected based on a ratio of a present idling-time required amount of air and an idling-time required amount of air in a new-vehicle condition.